Method of plating metals



Patented Oct. 6, 1931 UNITED STATES PATENT OFFICE WILLIAM E. WATKINS, F TUBE COMPANY, OF

NEW YORK, N. Y., ASSIGNOR TO COPPER PLATE SHEET 8: NEW YORK, N. Y., A CORPORATION OF NEW JERSEY METHOD OF PLATING METALS No nrawing. Application filed April 9,

1,197,694,1,197,695 and 1,256,084; and my 3 improved method also includes the further step of applying a second plating layer adhering to the first layer.

This application. is a continuation, in part, of my co-pending application Serial No.

260,803 filed March 10th, 1928.

This invention may be understood by considering its application to the plating of iron or steel sheets. In the production of a nonferrous covering on a ferrous base, the prescut universal practice is to take the iron or steel sheets from the hot rolls of the rolling mill, and stack them in piles in a Mesta pickler crate operated by a plunger which moves the crate up and down in an acid solution until all of the iron oxide on the sheets has been removed. The crate con taining the sheets or plates is then transferred to a bath of water. where it is plunged up and down until the plates have een thoroughly cleaned. The plates are then stacked in piles on an iron car and covered with an inverted iron pot, the interstices between the iron pot and the fioor of the car being chinked with sand to prevent admission of air. The car with its piles of plates is then pushed into what is commonly known as a box annealing oven, which is heated from 1400 F. to 1800 F. at the roof and left there until the temperature of the plates, if full finished stock, has been raised to approximately 1150 F. This annealing requires from 15 to 20 hours, depending upon the gauge of the plates. The heat is then turned off and the room with its contents i '59 allowed to cool sutficiently to permit removal I pickled before 1929. Serial No. 353,893.

of the car containing the plates. After removal from the annealing oven the plates are cooled to a temperature at which they will not oxidize when the inverted pot cover is removed, which cooling requires from 20 to 30 hours.

The above described operations are known as black pickling and black annealing. The latter operation is carried out for the purpose of removing the stresses set up in the plates by the rolling mill while being rolled from the sheet bar, and to make them soft enough to be fabricated. After receiving this treatment, and, if intended to be plated, I

theplates are cold rolled for the purpose of giving them a fine-grained surface. This rolling makes the plates too'hard to be fabricated, and they must again be annealed and they are usually passed into a receptacle known as a water bosh, containing water, in order to exclude the air from the surfaces of the plates until they are taken out and passed through a bath of molten non-ferrous metal. These latter operations are known as white annealing and white pickling.

The above described process, now in universal use, is both inefficient and wasteful. For instance, in the black and white pickling operations reliance is placed on the repeated plunging of the pickler crate to separate the plates sufliciently to permit the acid to remove all of the oxide. In order to secure satisfactory results, the black pickling should be continued for approximately 4 minutes and the white pickling for approximately 2 minutes. .This prolonged exposure of the.

plates to the action of the acid results in excessive loss of the ferrous metal. I have found, in actual commercial practice, that by using my improved method, it is not neces sary to expose the ferrous metal to the action of the acid for more than one minute, and the loss of ferrous metal is less than one-half of the loss occurring when present methods are employed.

The annealing of the plates in stacks or piles is not conducive to the production of a uniform product having the desired fabricating qualities, for it is impossible'to raise the ey can be plated, after which temperature of each plate, and of all parts of each plate, to the same value. The best annealing temperature is inthe neighborhood of 1620 F.; however, if an .attempt were made to raise the temperature of a stack or pile of full finished plates above 1150 F;, the surfaces of the plates would become soft enough to cause the plates to stick together. The present invention makes it possible to subject each plate to the proper annealing temperature, and being done singly the plates cannot stick together.

According to the present invention, the plates are given a preliminary treatment for the purpose of straightening them, for removing any oxides present on the surfaces thereof, and for imparting to the plates the desired surface characteristics. The plates are then covered with a plating mixture which is to become the first coating or plating layer on the ferrous plates. In general, the method of applying the first plating layer consists in covering the sheets with finely d1- vided plating material, such as finely divided copper or copper oxide carried by a suitable liquid, which provides a proper distributlon of the finely divided metal or oxide upon the plates, and maintains this distribution untilthe finely divided material, when subjected to heat, forms a. nonstripping union with the plates. The final step in my improved process consists in applying a second plating layer of metal adhering to the first layer.

I am aware that it has been proposed to coat a ferrous plate or sheet with a layer of copper or other non-ferrous metal, and then form a second plating layer over the first layer by passing the sheet through a molten bath. Such processes, however, have not been successful. The molten bath has a solvent action on the first plating layer, with the result that, in the processes heretofore practiccd, the first plating layer is practically destroyed. I have found that the magnitude of this solvent action is proportionate to the speed of travel of the plate or sheet through the molten metal, and the temperature of the 1 molten metal.

Heretofore it has been customary to pass the sheets, plates or strips through the molten bath at a speed of about 50 feet per minute. I have found that if a strongly adhering copper coating is first applied to the steel plates, sheets or strips by the process of my prior United States Patent No. 1,197,695, and the plates, sheet or strips passed'through a molten bath of tin or a mixture of tin and lead at a speed of 100 feet per minute the solvent effect on the copper coating is so little as to be permissible. If the speed is increased to 250 to 400 feet per minute, the solvent effect is negligible.

The numerous advantages of this invention, as compared with the plating process heretofore employed, will be apparent upon considering the following detailed descri tion, which sets forth the preferred embod ment of the invention and several sub-processes or steps of the preferred process, which may be used to advantage for other purposes than making composite plated metal of the character above described.

According to the present invention, the hot rolled plates are passed, one at a time, between rolls which straighten them and deliver them to a conveyor which travels through a shallow tank containing dilute acid. The plates are subjected to the action of the acid for a time and at a temperature sufiicient to remove the oxides on the surfaces of the plates. From the acid bath conveyor, the plates are conveyed through a water spray which washes the plates thoroughly. After the plates have been cleaned in this manner, they are passed between heated drying rolls. The plates are then covered with a plating mixture which ultimately becomes the first metal coating or plating layer on the iron plates. If it is so desired, the plates may be passed between heavy surfacing rolls before the plates are covered with the plating mixture, the object being to give the plates a fine grained, smooth surface.

The first step of the plating process proper, consists in applying to the article to be plated, a coating 0 finely divided plating material out of which a permanently adhering or nonstripping plating can be formed. If the articles are in the form of sheets, say of iron or steel, this initial coating may be applied by means of rotating rolls between which the sheets are passed. A coating machine which may be employed to advantage for this purpose is shown in my Patent No. 1,295,820. n general, this coating machine includes a mixing tank and a pair of coating rolls between which flat sheets may be passed to receive the viscous composition containing the finely divided metal or metal compound in suspension. The mixing tank contains an agitator for maintaining the proper homogeneity of the composition, and means is provided for pumping the agitated composition from the tank and spreading it on each of the coating rolls in a substantially uniform layer.

The next step in my process, consists in passing the plates, on a suitable conveyor,

through a furnace, whereby the coating composition yields a non-stripping or firmly adherent plating on the underlying iron, steel or the like. The furnace is preferably sealed against the free circulation of air, and in it the sheets as they pass through on an endless conveyor, are heated in a reducing atmosphere to a temperature and for the time necessary to form the plating from the materials of the coating composition. The plates are arched before they are passed into the furnace, the object being to support the plates out of contact with the furnace conthe plates.

The furnace conveyor delivers the plated sheets to a conveyor running through a cooling tube, and the latter conveyor delivers them to a third conveyor which transports them through a shallow tank containing dilute acid. The plates are then conveyed through a water spray Which washes them thoroughly and then dried.

The plates to which the copper plating has been applied are then conveyedthrough a molten bath of tin or a mixture of tin and lead. To prevent removal of the copper plating by the solvent action of the molten metal, the plates, sheets or strips are passed through the molten bath at a speed much higher than that heretofore employed in similar coating processes. The speed should be above 7 5 feet per minute, and preferably is between 250 to 400 feet per minute. At such s'peeds I have found that the molten metal does not remove the copper plating. This has been proved by scraping, or otherwise removing, the outer plating layer, and by examination, the copper plating has been found to be in substantially the same condition as it'was before the sheet or strip was passed through the molten bath.

Comparing the results of my process with prior methods, in passing a steel sheet, copper plated with 3 grammes of copper per square'foot by either of my three prior patents, through a bath of molten tin maintained at 550 F., (the temperature heretofore employed in commercialtinning operations in the production of tin plate,'at the maximum speed, F. P. M., found to pro- .duce a satisfactory film of tin) the corrosive,

or solvent action of the molten tin on the copper of the copper plated sheet is so great as to remove most all of the copper. I have discovered that this corrosive factor can be controlled to within permissible limits, by reducing the operating temperature of the molten tin to approximately 490 F., and increasing the speed of travel of the copper plated sheet through the molten'tin. I have found that at a speed of 100 F. P. M., the corrosive action is approximately percent less than at .50 F. P. M., while at a speed of from 250 to L00 F. P. M., the corrosive effeet on the copper is negligible. -At even the highest operating speeds I have found that the/tin will form asatisfactory fihn on the copper plated sheet and improve the continuityof the underlying copper film.

It will be noted that my improved process is continuousthroughout; the plates are coated successively, and conveyed through the annealing furnace in series, and are passed through the molten bath Without any interruption whatever in the process.

The finely divided plating material, appropriate for the purpose'of applying the ini- The vehicle employed forthe purpose of v spreading the finely divided ma erial uniformly over the sheets, may be any suitable liquid, preferably of a reducing character.

Oil, having an asphaltic base, is particularly suitable; and I have found that Mexican or Oklahoma crude petroleum having a specific gravity'corresponding to 7 to 7 7 lbs. to the gallon gives very satisfactory results.

This crude oil possesses the desired sprcading properties and the ability to hold the finely divided material in suspension; and its viscosity, reducing characteristics and cheapness render it particularly valuable for this purpose. In the event that a non-reducing vehicle is employed, I prefer to incorporate a reducing agent, such as finely divided'cars bon, the reducing agent being thoroughly mixed with the liquid and the plating material. Even when a reducing vehicle is employed, it is oftentimes desirable to add .a small quantity of a reducing agent to supplement the reducing action of the vehicle. A mixture having the proportions of 1 oz. of carbon to one pound of finely divided plating mixture and one pound of Mexican petroleum gives desirable results.

It Will beappreciated by those familiar with the metal plating art that various steps or parts of the preferred embodiment of my invention above described, maybe used to advantage for various purposes. For example, if it is desired to produce uncoated ferrous plates for fabricating purposes, the hot rolled plates may be straightened, treated with dilute acid to remove the oxides, and passed through the furnace and into cooling tubes without applying any plating mixture to the ferrous plates, these several steps being carried out in the manner above described. This process efiects uniform and simultaneous exposure of both surfaces of the plates to such temperatures as may be found to give the best annealing results, and this process makes it possible'to expose uniformly bothsurfacesod. is used,the plates are handled by handonly once,'instead of at least eight times when the ordinary process is employed.

This invention may be employed to great advantage in making plated metal by applying to ferrous plates, a single layer of plating metal. In order to accomplish this result, I prefer to subject the ferrous plates to 1 all of the steps described above, except the step of applying a plating mixture to the plates before they are conveyed into the furnace. Tin plate or other plated metal, produced in this manner, possesses superior fabricating qualities, due to the improved annealing treatment to which the plates are sub, ject; and it is much cheaper to manufacture plated metal in this manner than according to any process heretofore employed.

Some conception of the savings which may be effected by using this invention may be gained by considering the tin plating industry in the United States. In 1922, upwards of 56,000,000 pounds of metallic tin valued at approximately $25,000,00000 were used in the production of tin plate. In actual commercizfl practice, I have found that by first applying copper to the plate in the manner above described and then applying, by hot dipping, a coating of tin, a product is formed which is betterin quality and superior in lustre to tin plate made by any other known method; and the saving in the cost of plating metal is approximately 35%of the cost of the tin ordinarily used in plating the same quantity of ferrous'metal. In other words, if my process had been used in 1928, a net saving of about $l0,000,000.00 would have been effected in the cost of the plating metal alone. Even greater saving may be eifected by using cheaper metal than copper for the initial plating layer.

By employing my improved process, it is possible to effect a saving of one-half of the ferrous metal now lost in the black and white pickling operations, and one-half of the cost of the acid used in pickling the plates and of the cost of the labor required for these operations. It is also possible to save one-half of the cost of the fuel used in the annealing operations, and two-thirds of the cost of the labor ordinarily required for the black and white annealing. Also the improved process effects a saving of two-thirds of the cost of cold rolling the ferrous plates, and all of the expense of handling the plates into and out of the water bosh.

Ihave found, in actual commercial prac tice, that it is possihlc'fto produce an average of 90% primes bygiving the ferrous plates aprimary coating of copper and a secondary coating of tin, in the manner above described. lhe average number of primes produced according to the process now universally employed is less than 90%. The plated metal made according to this inventionis superior to ordinary plated metal, in quality and surface lustre. Any defects in the primary coatl ing, such as porosity or spots bare of plating lower melting point than the first metal, are cured by the secondary coating or layer of plating metal.

It is to be understood that this invention is not confined t0 the particular embodiments thereof above described, but includes such modifications thereof as fall within the scope of the appended claims.

I claim:

1. The process of lating metals, which consists of the following steps: applying to the metal to be plated a coating comprising a finely divided plating material, and a suitable liquid vehicle therefor; subjecting the metal to be plated together with the coating thereon to heat, the quantity of said coating and the intensity and duration of the heat being sufficient to form a plating layer of the plating metal adherent to the metal to be plated and subsequently applying a second plating layer of metal b passing the plated metal through a molten bath of a metal having a lower melting point than the first plating metal at a speed of from 250 to 400 feet per minute.

2. The process of plating metals, which consists of the following steps: applying to the metal to be plated a coating comprising a reducible compound of the plating metal, and asuitable reducing liquid vehicle therefor; subjecting the metal to be plated together with the coating thereon, to heat, the quantity of said coating and the intensity and duration of the heat being sufiicient to form a plating layer of the plating metal adherent 1 the metal to be plated; and subsequently applying a second plating layer of metal by passing the plated metal through a molten bath of a metal having a lower melting point than the first plating metal at a speed of from 250 to 400 feet per minute.

3. The process of plating metals, which consists-of the following steps: applying to the metal-to be plated acoating comprising a reducible compound of a latin a suitable liquid vehicle there or an a finely divided solid reducing agent; subjecting the metal to be plated, together with the coating thereon, to heat, the quantity of said coating and the intensity and duration of heat being sufficient to form a plating layer of the plating metal adherent to the metal'to be plated; and subsequently applying a second lating layer of metal by passing the plate vmetal through a molten bath of a metal having a latm metal at a speed of from 250 to 400 eet pe i minute. A

4. The process of plating metals, which consists of the following steps: applying to metal,

. plating metal adherent to the metal to be of said coating and the intensity and duration of the heat being sufiicient to form a plating layer of the plating metal adherent to the metal to be plated; and subsequently apply- ,5 ing a second plating layer of metal by passconsists of thefollowing steps: applying to the metal to he plated a coating comprising a reducible compound of the plating metal, a suitable liquid vehicle therefor, a finely divided solid reducing agent, and finely divided particles of the plating metal, subjecting the metal to be plated, together with the coating thereon to heat; the quantity of said coating and the intensity and duration of the heat being sufficient to form a plating layer of the plated-z and subsequently applying a second plating layer of metal by passing the plated metal through a molten bath of a metal having a lower melting point than the first plating metal-at a speed of'from 250 to 400 feet per minute.

6. The process of plating metals, which consists of the following steps: applying to the metal to be plated a coating comprising finely divided particles of the plating metal, and a suitable reducing liquid vehicle therefor: subjecting the metal to be plated, together with the coating thereon to heat, the quantity of said coating and the intensity and duration of the heat being suflicient to form.

a plating layer of the plating metal adherent 'to the metal to be plated; and subsequently applying a second plating layer of metal by bath of a metal having a lower melting point than the first plating metal at aspeed offrom,

250 to 400 feet per minute. I

7 The process of v plating metals, which consists of the following steps: applying to the metal to be plated a coating comprising finelv divided particles of the plating metal, a suitable liquid vehicle therefor, and a suitable finelv divided solid reducing agent; subs jecting the metal to be plated. together with the coating thereon to heat; the quantity of said coating and the intensity and duration of the heat being suflicient to form a plating layer of the plating metal adherent to the metal to be plated: and subsequentlv applying a second plating layer of metal bv passi us: the plated metal through a molten bath of a. metal having a lower melting point than the first plating metal at a speedof from 250 to 400 feet per minute.

8. The process of plating iron or steel which consistsof the following stepsrapplying to the metal to be plated, a coating comprising reducible compound of copper, a suitable reducing liquid vehicle therefor, subjecting passing the plated metal througha molten the metal to be plated, together with the coatng thereon, to heat, the quantity of said coat mg and the intensity and duration of the heat being suiiicient to form a plating layer of copper adherent to the metal to be plated; and subsequently. applying a second plating layer of metal by passing the plated metal through a molten-bath of a metal having a lower melting point than the first plating metal at a speed of from 250 to 400 feet per minute.

9. The proccssof plating iron or steel with copper and another metal, which consists of the following steps: applying to the metal to he plated a coating comprising a reducible compound of copper, a suitable liquid vehicle therefor, and a finely divided solid reducing agent, subjecting the metal to be plated, together with the coating thereon, to heat, the quantity of said coating, and the intensity and duration of the heat being sufficient to form a plating layer of copper adherent to themetal to he plated; and subsequently applying a second plating layer of metal by passmg the plated metal through a molten bath 0 a metal having a lower melting point than the first plating metal at a speed of from 250 to 400 feet per minute.

10. The process of plating metals which consists of the following steps: straightening hot rolled plates'from a rolling-mill, suhjecting the plates to the action of dilute acid,

subjecting the plates together with the coating thereon to heat, the quantity of said coating and the intensity and duration of the heat being suflicient to form a plating layer. of the plating metal adherent to the plates, and su sequentlyapplying to theplates a second plat: ing layer .of a metal'by passing the plated metal through a molten bath of a metal having a lower melting point than the first lating metal at a speed of from 250 to 400 eet per minute. i 11. The process of plating metals which consists of the following steps: applying to the metal to be plated a coating comprising a finely dividedplating material, and a suitable liquid-vehicle therefor, subjecting the metal to be plated, together with the coating thereon, to heat, the quantity of said coating and i the intensity and duration of the heat being suflicient to form aplating layer of the plating metal adherent to the metal to be plated; subjecting the plated metal to the action of dilute acid; washing the 'lated metal to remove the acid; and applying .to the plated metal a second plating layer of-m'etal by passing the plated'metal through a molten bath of a metal having a lower melting point that the firstplating metal at a speed of from 250 to 400 feet per minute. h

12. The process of forming a compound plating on a ferrous metal base which comprises, first, subjecting the ferrous metal base, while in surface contact with a compound of copper to a temperature above the melting 5 oint of copper, and suflicient to raise the errous metal approximately to a welding heat, thereby converting the copper compound into metallic copper in the shape of a substantially continuous plating layer fused to the ferrous metal and forming an exterior protective layer containing magnetic oxide of iron; second, removing said layer containing oxide of iron; and, third, passlng the ferrous metal so plated with copper through a molten bath of a metal having a lower melting point than the first plating metal at a speed of from 250 to 400 feet per minute.

13. The process of plating metals which consists of the following steps: applying to the metal tobe plated a coating composition of a reducible compound of a plating metal, a suitable liquid vehicle therefor and a finely divided solid reducing agent; subjecting the metal to be plated together with the coating thereon to heat, the quantity of said coating and the intensity and duration of heat being, sufiicient to form a plating layer of the plating metal adhering to the metal to be plated; and subsequently applying a second plating layer of metal by passin the plated metal through a molten bath 0 a metal having a lower melting point than the first platmg metal at a speed'of at least 75 feet per minute. 14. The process of applying iron or steel which consists of the following steps: applying to the metal to be plated a coating composition comprising a reducible compound of copper, and a suitable reducing liquid vehicle therefor; subjecting the metal to be plated, together with the coating thereon to heat the quantity of said coatin and the intensity and the duration of the1eat being sufficient to form a-plating layer of copper adhering to the metal to be plated; and subsequently applying-a second plating layer of metal by passin the plated metal through a molten bath 0 a metal havin a lower melting point than copper at a speed of at least 75. feet per minute. a i

In testimon whereof I afiix my signature;

VH2LIAM E. WATKINS. 

